The invention relates to cellular telephone systems, and particularly to systems which avoid the need for a serviceman to have physical access to a mobile cellular telephone unit in order to connect or disconnect various telephone features, parameters, etc.
Cellular telephone systems are very commonplace, and typically include a mobile telephone switching office (MTSO) which couples a "land side" telephone to a "cell site" facility that includes a transmitter, a receiver, filtering circuitry, and control equipment. Various mobile cellular telephone units, hereinafter referred to as "mobile telephones", communicate with the cell site via assigned rf channels. A number of overlapping cell sites usually are spaced throughout a metropolitan area. As a particular mobile unit moves out of the range of one cell site into the range of another, automatic "hand-off" operations occur as a result of continuous communication between the various cell sites and mobile telephones on a "voice channel". Voice communication on a "voice channel" occurs between the user of each mobile telephone and "land side" telephones through the cell sites and the MTSO.
Mobile telephones frequently are sold or leased by distributors. The mobile telephones contain software "feature switches" that allow the subscriber to be assigned a telephone number and have various operating features and parameters such as hands-free operation, repertory memory storage, auxiliary horn/light alert capability, call-in absence indicator, call restrictions (i.e., local calls only), theft alarm, and provision of a dealer security code. The subscriber's fee may increase according to the number of such features that are switched on. Ordinarily, the mobile telephone unit is taken to a service shop. The serviceman plugs in a test set to access the various feature switches and set up the mobile telephone for use with the features desired by the subscriber. The parameters and feature selection information are entered through the test set. The test set then is disconnected, and the mobile telephone unit is ready for use.
A long-standing problem is that some subscribers do not pay their monthly bills for the cellular telephone service. There exists no convenient way for the cellular telephone company to terminate service to non-paying subscribers without gaining access to the non-paying subscribers' mobile telephones. Since the "breakup" of AT&T, there are many different corporate suppliers of mobile telephone services. After a non-paying subscriber runs up an unpaid bill with one supplier, he can subscribe to another for a while, and then another, and get away without paying.
More than a dozen years ago, the Electronic Industry Associates (EIA) defined a "standard" message format for programming of feature switches for cellular mobile telephones. However, the various telephone companies have been unable to agree on message formats for programming of feature switches, and it has been impractical to adapt mobile telephone switching offices (MTSO's) to accommodate various formats for feature switch programming messages.
It would be highly desirable to provide a system which enables suppliers of cellular telephone service to connect or disable certain mobile cellular telephone units and to set feature switches thereof without having to modify MTSO's.